In case of capacitive approximation sensors, the approximation of an object to a sensor zone is substantially measured without contact by generating and measuring alternating electrical fields. Functions, such as switching functions, of an electrical device, particularly of an electrical hand-held device, can be derived from the measuring signal.
A measuring principle known from prior art for the detection of an approximation to a sensor zone uses a capacitive approximation sensor with two sensor electrodes. The sensor electrodes of the capacitive approximation sensor can be coupled capacitively, i.e. an alternating electrical field is emitted at a sensor electrode, which couples into the other sensor electrode via an approximating object in case an object approximates to the sensor electrodes. This way, a capacitive path is generated between a transmitter and a receiver. This method is generally known as transmission method. Two electrodes form a sensor zone.
There is a need to provide several sensor zones, for instance, at an electrical hand-held device, wherein each sensor zone has a different function or functionality in case an object approximates to a sensor zone. The sensor devices known from prior art, which are operated according to the transmission method mentioned before, require two electrodes for each sensor zone. This means that n sensor zones require twice the number (n) of sensor electrodes.
The transmission method known from prior art proves to be disadvantageous, since each sensor zone which requires two sensor electrodes, respectively, requires a separate or multiplexed transmitting and receiving path in addition to the required electric circuit required for this, which particularly has an impact on the power consumption of a capacitive sensor device being used to monitor several sensor zones. Furthermore, an individual transmission measuring has to be performed for each sensor zone in order to detect an approximation to the respective sensor zone as far as the transmission method known from prior art is concerned.